This invention relates to heating installations for vehicles, in particular motor vehicles, and more particularly to air conditioning installations for motor vehicles, having an evaporator which is used as a source of heat when the installation is operating in a heating mode.
More specifically still, the invention relates to an air conditioning installation for the cabin of a motor vehicle, comprising a refrigerant fluid circuit having three branches, namely a first branch, a second branch and a third branch, with an evaporator and a compressor being connected in the first branch, with the compressor downstream of the evaporator; a condenser is arranged in the second branch, and there is no condenser in the third branch. The second and third branches are connected in parallel with each other in such a way that the first and second branches together constitute a cooling loop, while the first and third branches together constitute a heating loop. A first expansion device is interposed in the cooling loop between the condenser and the evaporator; and flow control means, typically in the form of at least one stop or changeover valve, are also provided for passing fluid leaving the first branch into either the second or the third branch. Finally, the installation also includes means for passing air into the cabin of the vehicle after the air has undergone heat exchange with the evaporator.
An installation of the above specific type is known from French patent specification No. FR 2 717 126 A, in which the thermal energy generated in the heating loop is determined by the mass flow of fluid produced by the compressor, which is itself a function of the speed at which the compressor is driven, and therefore of the prevailing running speed of the engine of the vehicle. The heating power available can under these circumstances be less than that which is necessary for heating of the cabin. In particular, at the time when the engine is being started from cold under cold weather conditions, the initial density of the fluid in the air conditioning circuit, and consequently the fluid mass flow produced by the compressor, is usually insufficient to provide satisfactory heating.
The object of the invention is to overcome these drawbacks, and to enable the thermal energy produced to be matched to the demand for heating, especially at low ambient temperatures.
According to the invention, an air conditioning installation for the cabin of a motor vehicle, comprising a refrigerant fluid circuit having a first branch containing an evaporator followed by a compressor, a second branch containing a condenser, and a third branch not containing a condenser, the second and third branches being connected in parallel with each other so that they respectively constitute, with the first branch, a cooling loop which also contains a first expansion device interposed between the condenser and the evaporator, and a heating loop, with flow control means being provided for sending the fluid leaving the first branch into either the second branch or the third branch, the installation further including means for sending into the cabin air which has exchanged heat with the evaporator, wherein the installation further includes flow varying means for causing the quantity of fluid flowing in the heating loop to be varied according to demand, the flow varying means comprising limiting means for interrupting or momentarily restricting the flow of the fluid in the third branch, whereby to permit the compressor to draw fluid from the second branch, and discharge means for putting the second branch into momentary communication with the outlet of the compressor.
In some embodiments of the invention, the flow control means comprise a first valve connected in the second branch upstream of the condenser, and a second valve connected in the third branch, the valves being connected to a control unit for controlling the valves.
In other embodiments, the flow control means comprise a three-way valve defining a first fluid path from the downstream end of the first branch to the upstream end of the second branch, and a second fluid path from the downstream end of the first branch to the upstream end of the third branch, the valve being connected to a control unit for controlling the valve.
The flow control means preferably include means for measuring the pressure of the fluid at the outlet of the compressor, the measuring means being connected to the control unit.
According to a preferred feature of the invention, the limiting means comprises a differential pressure regulator interposed in the third branch and constituting a second expansion device for authorizing passage of the fluid only when the difference in pressure between its inlet and its outlet exceeds a predetermined threshold value.
In a preferred arrangement where the flow control means comprise a first valve connected in the second branch upstream of the condenser, and a second valve connected in the third branch, the valves being connected to a control unit for controlling the valves, the limiting means include the second valve, which is arranged to be closed by the control unit in response to a low pressure detected by the measuring means. With this arrangement, the third branch may include a constriction downstream of the second valve, the constriction constituting a second expansion device.
According to another preferred feature of the invention, the discharge means comprises a bypass duct bypassing the flow control means, with an over-pressure relief valve interposed in the bypass duct, whereby fluid leaving the compressor can be passed to the second branch.
With this last mentioned arrangement, and where the flow control means comprises a first valve connected in the second branch upstream of the condenser, and a second valve connected in the third branch, the valves being connected to a control unit for controlling the valves, the bypass duct may be connected in parallel with the first valve. Alternatively, the bypass duct may be connected between the output of the second valve and the output of the first valve.
In other embodiments of the installation according to the invention which includes a bypass duct and over-pressure release valve as defined above, and in which the flow control means comprises a three-way valve defining a first fluid path from the downstream end of the first branch to the upstream end of the second branch, and a second fluid path from the downstream end of the first branch to the upstream end of the third branch, the three-way valve being connected to a control unit for controlling the valve, the bypass duct is connected between one of the two sides of the three-way valve that are connected to the first and third branches respectively, and the side of the three-way valve that is connected to the second branch.
In embodiments of the invention in which the flow control means include measuring means for measuring the fluid pressure at the compressor outlet, the measuring means being connected to a control unit, the flow control means further including a first valve connected in the second branch upstream of the condenser, and a second valve connected in the third branch, the valves being connected to the control unit for control of the valves, the discharge means are adapted to cause momentary opening of the first valve by the control unit, as a function of the pressure in the fluid as detected by the measuring means, whereby to enable fluid leaving the compressor to be passed to the second branch.
With this last mentioned arrangement, the discharge means may be adapted to compare the pressure in the fluid as detected by the measuring means with a maximum threshold value of pressure, and to cause the first valve to be opened momentarily when the detected pressure exceeds the threshold value. In addition, a non-return valve is preferably disposed in the second branch downstream of the condenser and either upstream or downstream of the first expansion device.
Alternatively, the discharge means may be adapted to compare the fluid pressure detected by the measuring means with a datum value of pressure computed by the control unit as a function of heating demand, and to cause the first valve to open momentarily when the detected pressure exceeds the datum value.
According to another preferred feature of the invention, the first expansion device is a thermostatic expansion device disposed in the second branch downstream of the condenser.
Preferably, the first expansion device is a calibrated orifice disposed in the second branch downstream of the condenser, and a fluid accumulator is disposed in the first branch between the evaporator and the compressor.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which is given by way of non-limiting example only and with reference to the accompanying drawings.